Laminated sheet and food packaging container

Abstract

To provide a laminated sheet having high cold resistance while having excellent heat resistance and moldability.SOLUTION: A laminated sheet comprises an inner layer and an outer layer. The inner layer contains a thermoplastic resin and an inorganic substance powder with a mass ratio of 10:90-60:40. The thermoplastic resin contains a polypropylene resin and a polyethylene-based resin. The polypropylene resin contains a first propylene-ethylene block copolymer and / or a propylene homopolymer, and the polyethylene-based resin contains linear low-density polyethylene and high-density polyethylene. Based on the total amount of the thermoplastic resin, a content of the first propylene-ethylene block copolymer and / or the propylene homopolymer is 30 mass% or more and 50 mass% or less, a content of the linear low-density polyethylene is 30 mass% or more and 57 mass% or less, and a content of the high-density polyethylene is 3 mass% or more and 30 mass% or less. The outer layer contains a second propylene-ethylene block copolymer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a laminated sheet and a food packaging container.

Background Art

[0002] Conventionally, polyolefin resin sheets and their molded articles have been used, for example, in food packaging containers from the viewpoint of excellent moldability.

[0003] In recent years, attempts have been made to reduce the content of resin components in resin molded articles from the viewpoint of environmental protection. As such an attempt, increasing the content of inorganic substances (such as calcium carbonate) in resin molded articles has been studied.

[0004] As a polyolefin resin sheet used for such resin molded products, for example, a laminated sheet having an inner layer in which calcium carbonate is highly filled in a polyolefin-based resin and an outer layer containing a polyolefin-based resin is known (for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, food packaging containers are required to have not only heat resistance to withstand heating by a microwave oven but also cold resistance to withstand frozen storage. Although the resin sheets of Patent Documents 1 and 2 have good heat resistance, further improvement in cold resistance is required.

[0007] In addition, a resin sheet highly filled with an inorganic substance powder such as calcium carbonate is likely to have significantly deteriorated moldability as compared with a resin sheet made of only a polyolefin-based resin. In particular, when the outer layer is thin, the appearance of the inner layer surface may have an adverse effect on the appearance of the resin molded product (for example, a food packaging container). Further, a resin molded product highly filled with an inorganic substance powder is likely to have a reduced impact strength and reduced cold resistance at low temperatures as compared with a resin molded product made of only a polyolefin-based resin.

[0008] The present invention has been made in view of these circumstances, and an object thereof is to provide a laminated sheet and a food packaging container having good heat resistance and moldability and high cold resistance.

Means for Solving the Problems

[0009] The above problems can be solved by the following configuration.

[0010] [1] A laminated sheet having an inner layer and two outer layers laminated on both surfaces of the inner layer, wherein the inner layer contains a thermoplastic resin and an inorganic substance powder in a mass ratio of 10:90 to 60:40, and the thermoplastic resin contains a polyethylene-based resin and a polypropylene-based resin in a mass ratio of 7:3 to 5:5. The polyethylene-based resin contains linear low-density polyethylene and high-density polyethylene, and the polypropylene-based resin contains a first propylene-ethylene block copolymer and / or a propylene homopolymer. The content of the linear low-density polyethylene is 30% by mass or more and 57% by mass or less, the content of the high-density polyethylene is 3% by mass or more and 30% by mass or less, and the content of the first propylene-ethylene block copolymer and / or the propylene homopolymer is 30% by mass or more and 50% by mass or less, based on the total amount of the thermoplastic resin. Each of the two outer layers contains a second propylene-ethylene block copolymer. [2] The laminated sheet according to [1], wherein the polypropylene-based resin is composed of a first propylene-ethylene block copolymer. [3] The inner layer is the laminated sheet according to [1], which contains a thermoplastic resin and an inorganic substance powder in a mass ratio of 10:90 to 50:50. [4] The MFR(2) of the second propylene-ethylene block copolymer measured at 230 °C and 2.16 kg according to JIS K 6921-2:2018 (ISO19069-2:2016) is higher than the MFR(1) of the first propylene-ethylene block copolymer measured at 230 °C and 2.16 kg in accordance with JIS K 6921-2:2018 (ISO19069-2:2016). The laminated sheet according to [2]. [5] The ratio of the MFR(2) to the MFR(1) (MFR(2) / MFR(1)) is 3.0 or more. The laminated sheet according to [4]. [6] The MFR(1) is 0.2 g / 10 min or more and 0.5 g / 10 min or less, and the Charpy impact strength (notched) at -20 °C in accordance with JIS K 6921-2:2018 (ISO19069-2:2016) of the first propylene-ethylene block copolymer is 7.8 kJ / m 2 or more and 11.8 kJ / m 2 or less. The laminated sheet according to [4]. [7] The MFR(2) is 0.7 g / 10 min or more and 2.7 g / 10 min or less, and the Charpy impact strength (notched) at -20 °C in accordance with JIS K 6921-2:2018 (ISO19069-2:2016) of the second propylene-ethylene block copolymer is 5.0 kJ / m 2 or more and 9.0 kJ / m 2 or less. The laminated sheet according to [4]. [8] The MFR(L) of the linear low-density polyethylene measured at 190 °C and 2.16 kg according to JIS K 6922-2:2018 (ISO17855-2:2016) is 0.7 g / 10 min or more and 1.7 g / 10 min or less. The laminated sheet according to [1]. [9] The laminated sheet according to [1], wherein the MFR (H) measured at 190 ° C and 21.6 kg in accordance with JIS K 6922-2:2018 (ISO 17855-2:2016) of the high-density polyethylene is 3.0 g / 10 min or more and 7.0 g / 10 min or less.

[10] The laminated sheet according to [1], wherein the inorganic substance powder is heavy calcium carbonate.

[11] The laminated sheet according to

[10] , wherein the average particle diameter of the heavy calcium carbonate is 0.7 μm or more and 6.0 μm or less.

[12] The laminated sheet according to [1], wherein the thicknesses of the two outer layers are each 2.0% or more and 10.0% or less of the total thickness of the laminated sheet.

[13] A food packaging container comprising the laminated sheet according to any one of [1] to

[12] .

Effect of the Invention

[0011] According to the present invention, it is possible to provide a laminated sheet and a food packaging container having good heat resistance and moldability while having high cold resistance.

Mode for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail based on embodiments. However, the present invention is not limited to these embodiments.

[0013] As a result of intensive studies, the present inventors have found that 1) by containing a propylene-ethylene block copolymer and / or a propylene homopolymer in the inner layer and a propylene-ethylene block copolymer in the outer layer, and 2) by containing a larger amount of linear low-density polyethylene (LLDPE) than high-density polyethylene (HDPE) in the inner layer, it is possible to improve the cold resistance while maintaining the moldability and heat resistance even in a laminated sheet containing a large amount of inorganic substance powder.

[0014] Although this mechanism is not clear, it is presumed as follows. The inner layer contains a propylene-ethylene block copolymer and / or a propylene homopolymer, and the outer layer contains a propylene-ethylene block copolymer. By including a relatively large amount of linear low-density polyethylene (LLDPE) as the polyethylene-based resin in the inner layer, it is possible to enhance the low-temperature impact resistance (cold resistance) while maintaining heat resistance. On the other hand, as the low-temperature impact resistance increases, for example, drawdown is likely to occur in vacuum formability, and the formability is easily impaired. In contrast, by further including high-density polyethylene (HDPE), preferably HDPE with a low melt flow rate (MFR), as the polyethylene in the inner layer, a decrease in formability can be suppressed.

[0015] Hereinafter, the configuration of the laminated sheet of the present invention will be described in detail.

[0016] 1. Laminated Sheet The laminated sheet according to an embodiment of the present invention has an inner layer and two outer layers laminated on both sides thereof.

[0017] 1-1. Inner Layer The inner layer contains a thermoplastic resin and an inorganic substance powder.

[0018] The content ratio of the thermoplastic resin to the inorganic substance powder is such that the thermoplastic resin:inorganic substance powder is 10:90 to 60:40 (mass ratio), preferably 10:90 to 50:50 (mass ratio), and more preferably 20:80 to 45:55 (mass ratio). The higher the content ratio of the inorganic substance powder, the lower the content ratio of the resin component in the laminated sheet can be, and thus the environmental load can be further reduced.

[0019] 1-1-1. Thermoplastic Resin The thermoplastic resin includes a polyethylene-based resin and a polypropylene-based resin.

[0020] The content ratio of the polyethylene resin and the polypropylene resin is such that polyethylene resin: polypropylene resin is 7:3 to 5:5 (mass ratio), preferably 6:4 to 5:5. The higher the content ratio of the polyethylene resin, the higher the cold resistance of the laminated sheet can be enhanced.

[0021] (1) Polyethylene resin The polyethylene resin is a resin having a component unit derived from ethylene as a main component. Having a component unit derived from ethylene as a main component means that the content of the component unit derived from ethylene is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more with respect to the polyethylene resin. In addition, the polyethylene resin may further contain a component unit derived from an α-olefin as necessary. Examples of the α-olefin include α-olefins having 3 to 10 carbon atoms (propylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, etc.).

[0022] The polyethylene resin includes linear low density polyethylene (LLDPE) and high density polyethylene (HDPE).

[0023] (Linear low density polyethylene (LLDPE)) Linear low density polyethylene (LLDPE) refers to polyethylene having a density of 0.900 g / cm 3 or more and less than 0.940 g / cm 3 , preferably 0.900 g / cm 3 or more and less than 0.928 g / cm 3 . Linear low density polyethylene can easily enhance the low temperature impact resistance of the laminated sheet and can enhance the cold resistance.

[0024] The melt flow rate (MFR) (also referred to as MFR(L)) of linear low-density polyethylene according to JIS K 6922-2:2018 (ISO17855-2:2016) at 190°C and 2.16 kg is not particularly limited, but is preferably 0.7 g / 10 min or more and 1.7 g / 10 min or less. When the MFR of linear low-density polyethylene is 0.7 g / 10 min or more, the cold resistance of the laminated sheet can be further enhanced. When the MFR of linear low-density polyethylene is 1.7 g / 10 min or less, the vacuum formability of the laminated sheet can be less impaired. From the same perspective, the MFR of linear low-density polyethylene is more preferably 0.9 g / 10 min or more and 1.4 g / 10 min or less.

[0025] The content of linear low-density polyethylene in the inner layer is 30% by mass or more and 57% by mass or less based on the total amount of the thermoplastic resin contained in the inner layer. When the content of linear low-density polyethylene is 30% by mass or more, the proportion of linear low-density polyethylene is relatively higher than that of high-density polyethylene, so the cold resistance of the laminated sheet can be further enhanced. When the content is 57% by mass or less, the proportion of high-density polyethylene can be kept at a certain level or more, so the vacuum formability of the laminated sheet is less likely to be impaired. From the same perspective, the content of linear low-density polyethylene is more preferably 35% by mass or more and 52% by mass or less.

[0026] (High-density polyethylene (HDPE)) High-density polyethylene (HDPE) is polyethylene with a density of 0.942 g / cm 3 or more. High-density polyethylene can more easily enhance the mechanical strength of the laminated sheet and improve the vacuum formability.

[0027] The MFR (at 190°C, 21.6 kg) (also referred to as MFR(H)) of high-density polyethylene according to JIS K 6922-2:2018 (ISO17855-2:2016) is not particularly limited, but for example, it is preferably 3.0 g / 10 min or more and 7.0 g / 10 min or less. When the above MFR of high-density polyethylene is 3.0 g / 10 min or more, the cold resistance of the laminated sheet can be further enhanced. When the above MFR of high-density polyethylene is 7.0 g / 10 min or less, the vacuum formability of the laminated sheet can be made less likely to be impaired. From the same perspective, the above MFR of high-density polyethylene is more preferably 4.0 g / 10 min or more and 6.0 g / 10 min or less.

[0028] The content of high-density polyethylene in the inner layer is 3% by mass or more and 30% by mass or less based on the total amount of the thermoplastic resin contained in the inner layer. When the above content of high-density polyethylene is 3% by mass or more, the molding processability of the laminated sheet can be further enhanced. When the above content is 30% by mass or less, the cold resistance of the laminated sheet is less likely to be impaired. From the same perspective, the above content of high-density polyethylene is more preferably 10% by mass or more and 20% by mass or less.

[0029] From the perspective of achieving both cold resistance and vacuum formability, the content ratio of linear low-density polyethylene to high-density polyethylene can preferably be 1:8 to 1:1 (by mass ratio), more preferably 1:5 to 1:2 (by mass ratio).

[0030] (Other polyethylene) The polyethylene-based resin may further contain other polyethylenes other than the above, as long as the effects of the present invention are not impaired. Examples of other polyethylenes include medium-density polyethylene (MDPE), low-density polyethylene (LDPE), ultra-low-density polyethylene (ULDPE), ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-butene-1 copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-octene-1 copolymer, etc.

[0031] Note that medium-density polyethylene (MDPE) is polyethylene having a density of 0.930 g / cm 3 or more and less than 0.942 g / cm 3 Low-density polyethylene (LDPE) is polyethylene having a density of 0.910 g / cm 3 or more and less than 0.930 g / cm 3 Ultra-low-density polyethylene (ULDPE) is polyethylene having a density of less than 0.910 g / cm 3 .

[0032] (2) Polypropylene-based resin A polypropylene-based resin is a resin having a component unit derived from propylene as a main component. Having a component unit derived from propylene as a main component means that the content of the component unit derived from propylene is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more with respect to the polypropylene-based resin. The polypropylene-based resin includes a first propylene-ethylene block copolymer.

[0033] (First propylene-ethylene block copolymer) The first propylene-ethylene block copolymer is a copolymer including a propylene block and an ethylene block.

[0034] The content of the propylene block is preferably 40% by mass or more and 85% by mass or less, and more preferably 50% by mass or more and 75% by mass or less with respect to the total amount of the propylene block and the ethylene block. When the content of the propylene block is at or above the lower limit value, the heat resistance of the laminated sheet can be further enhanced. When the content of the propylene block is at or below the upper limit value, since the content of the ethylene block is at a certain level or more, the cold resistance of the laminated sheet can be further enhanced.

[0035] That it is a block copolymer can be confirmed by fractional-NMR·GPC analysis.

[0036] The weight average molecular weight of the propylene block is preferably, for example, 100,000 or more and 200,000 or less. The weight average molecular weight of the ethylene block is preferably, for example, 50,000 or more and 150,000 or less. When the average molecular weight of the propylene block or the ethylene block is within the above range, the characteristics of each block are more likely to be expressed, and the heat resistance and cold resistance can be further enhanced.

[0037] The MFR(1) of the first propylene-ethylene block copolymer measured at 230 °C and 2.16 kg according to JIS K 6921-2:2018 (ISO19069-2:2016) is preferably lower than the MFR(2) of the second propylene-ethylene block copolymer described below. Specifically, the above MFR(1) of the first propylene-ethylene block copolymer is preferably 0.1 g / 10 min or more and 1.0 g / 10 min or less, and more preferably 0.2 g / 10 min or more and 0.5 g / 10 min or less. When the above MFR of the first propylene-ethylene block copolymer is 0.2 g / 10 min or more, the cold resistance of the laminated sheet can be further enhanced. When the above MFR is 0.5 g / 10 min or less, the heat resistance of the laminated sheet can be further maintained.

[0038] The Charpy impact strength (notched) at -20 °C of the first propylene-ethylene block copolymer according to JIS K 6921-2:2018 (ISO19069-2:2016) is 7.8 kJ / m 2 or more and 11.8 kJ / m 2 or less, preferably 8.0 kJ / m 2 or more and 11.6 kJ / m 2 or less, and more preferably. When the above Charpy impact strength (notched) of the first propylene-ethylene block copolymer is at least the lower limit value, the cold resistance of the laminated sheet can be further enhanced. When the above Charpy impact strength (notched) is at most the upper limit value, the heat resistance of the laminated sheet can be further maintained.

[0039] The content of the first propylene-ethylene block copolymer in the inner layer is 30% by mass or more and 50% by mass or less based on the total amount of the thermoplastic resin contained in the inner layer. When the content is 30% by mass or more, the mechanical strength and heat resistance of the laminated sheet can be further enhanced. When the content is 50% by mass or less, the cold resistance of the laminated sheet is less likely to be impaired. From the same perspective, it is more preferable that the content of the first propylene-ethylene block copolymer is 35% by mass or more and 45% by mass or less.

[0040] The first propylene-ethylene block copolymer may further contain a block or a component unit derived from other α-olefins other than the propylene block and the ethylene block, as long as the effects of the present invention are not impaired. Examples of other α-olefins include α-olefins having 4 to 10 carbon atoms (1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, etc.). The content of other component units is preferably 10% by mass or less based on the copolymer.

[0041] (Other polypropylenes) The polypropylene-based resin may further contain other polypropylenes other than the first propylene-ethylene block copolymer or the propylene homopolymer, as long as the effects of the present invention are not impaired. Examples of other polypropylenes include propylene random copolymers (for example, ethylene-propylene random copolymers, butene-1-propylene random copolymers, ethylene-butene-1-propylene random terpolymers).

[0042] 1-1-2. Inorganic substance powder The type of the inorganic substance powder is not particularly limited. Examples of the inorganic substance powder include carbonates, sulfates, silicates, phosphates, or borates of metals (calcium, magnesium, aluminum, titanium, iron, zinc, etc.); oxides of the above metals; hydrates of the above salts or oxides, etc. The inorganic substance powder can be used alone or in combination of two or more.

[0043] Specific examples of the inorganic substance powder include powders such as calcium carbonate, magnesium carbonate, zinc oxide, titanium oxide, silica, alumina, clay, talc, kaolin, aluminum hydroxide, magnesium hydroxide, aluminum silicate, magnesium silicate, calcium silicate, aluminum sulfate, magnesium sulfate, calcium sulfate, magnesium phosphate, barium sulfate, silica sand, carbon black, zeolite, molybdenum, diatomaceous earth, sericite, shirasu, calcium sulfite, sodium sulfate, potassium titanate, bentonite, and graphite.

[0044] Among them, calcium carbonate particles are preferred. The calcium carbonate particles may be either heavy calcium carbonate particles or light calcium carbonate particles. From the viewpoint of being more likely to form a larger contact interface with the thermoplastic resin and more easily improving the mechanical properties of the laminated sheet, etc., it is preferable that the inorganic substance powder contains heavy calcium carbonate particles.

[0045] Heavy calcium carbonate is calcium carbonate obtained by mechanically pulverizing (dry method, wet method, etc.) natural raw materials (such as limestone) mainly composed of CaCO3. Light calcium carbonate is calcium carbonate prepared by a synthetic method (such as a chemical precipitation reaction).

[0046] The inorganic substance powder may or may not be surface-treated. Among them, from the viewpoint of hygroscopicity, it is preferable that the inorganic substance powder is not surface-treated.

[0047] The shape of the inorganic substance powder is not particularly limited and may be any of particulate (spherical, irregular shape, etc.), flaky, granular, fibrous, etc.

[0048] The average particle diameter of the inorganic substance powder is not particularly limited, preferably 0.1 μm or more and 50.0 μm or less, more preferably 0.5 μm or more and 13.5 μm or less, and still more preferably 0.7 μm or more and 6.0 μm or less. When the average particle diameter of the inorganic substance powder is 0.1 μm or more, it is easier to disperse the inorganic substance powder in the thermoplastic resin. When the average particle diameter of the inorganic substance powder is 50.0 μm or less, it is possible to less easily impair the appearance of the laminated sheet. The average particle diameter of the inorganic substance powder means a value calculated from the measurement result of the specific surface area by the air permeability method according to JIS M-8511. As the measuring device, for example, the specific surface area measuring device SS-100 type manufactured by Shimadzu Corporation can be preferably used.

[0049] 1-1-3. Other Components The inner layer may further contain other components other than the thermoplastic resin and the inorganic substance powder as long as the effects of the present invention are not impaired. Examples of other components include lubricants, dispersants, antistatic agents, antioxidants, heat stabilizers, ultraviolet absorbers, colorants, plasticizers, and the like. Among them, since the inner layer contains a large amount of inorganic substance powder, it is preferable to contain a lubricant or an antioxidant.

[0050] Examples of lubricants include fatty acids such as stearic acid, hydroxystearic acid, composite stearic acid, and oleic acid; aliphatic alcohols; aliphatic amides such as stearamide, oxystearamide, oleylamide, erucylamide, ricinoleamide, behenamide, methylolamide, methylenebisstearamide, methylenebisstearobehenamide, bisamide acids of higher fatty acids, and composite amides; aliphatic esters such as n-butyl stearate, methyl hydroxystearate, polyhydric alcohol fatty acid esters, saturated fatty acid esters, and ester waxes; fatty acid metal soaps such as zinc stearate and magnesium stearate.

[0051] Examples of antioxidants include phosphorus-based antioxidants and phenol-based antioxidants. Examples of phosphorus-based antioxidants include phosphites such as triphenyl phosphite, tris(nonylphenyl) phosphite, tris(2,4-di-t-butylphenyl) phosphite; and phosphates such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate. The phenolic antioxidant is preferably a hindered phenolic antioxidant. Examples of hindered phenolic antioxidants include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, etc. These can be used alone or in combination of two or more.

[0052] The content of other components in the inner layer is not particularly limited, but is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.5% by mass or more and 3.0% by mass or less, based on the inner layer.

[0053] 1-1-4. Physical properties of the inner layer The thickness of the inner layer is not particularly limited, but is preferably 80.0% or more and 96.0% or less based on the total thickness of the laminated sheet, for example. When the ratio of the thickness of the inner layer is 80.0% or more, the characteristics of the inner layer can be more easily exhibited. On the other hand, when the ratio of the thickness of the inner layer is 96.0% or less, the ratio of the thickness of the outer layer can be made a certain value or more, so that the concealability of the inner layer containing a large amount of inorganic substance powder can be further enhanced and the appearance can be improved.

[0054] The thickness of the inner layer is preferably 50 μm or more and 900 μm or less, more preferably 80 μm or more and 850 μm or less, for example.

[0055] 1-2. Outer layer The two outer layers are respectively disposed on one surface and the other surface of the inner layer. The composition and physical properties of the outer layer disposed on one surface of the inner layer and the outer layer disposed on the other surface may be the same or different. Each of the two outer layers contains a second propylene-ethylene block copolymer.

[0056] 1-2-1. Second propylene-ethylene block copolymer As the second propylene-ethylene block copolymer contained in the outer layer, the same ones as those listed as the first propylene-ethylene block copolymer contained in the inner layer can be used. The second propylene-ethylene block copolymer contained in the outer layer may be the same as or different from the first propylene-ethylene block copolymer contained in the inner layer. Among them, from the viewpoint of suppressing roughening of the interface between the inner layer and the outer layer, further reducing the color unevenness of the wood grain tone of the laminated sheet, and improving the appearance, the second propylene-ethylene block copolymer contained in the outer layer is preferably different from the first propylene-ethylene block copolymer contained in the inner layer, and more preferably has different MFRs.

[0057] The MFR(2) of the second propylene-ethylene block copolymer contained in the outer layer, measured at 230 °C and 2.16 kg according to JIS K 6921-2:2018 (ISO19069-2:2016), is preferably higher than the MFR(1) of the first propylene-ethylene block copolymer contained in the inner layer. That is, the ratio of MFR(2) to MFR(1) (MFR(2) / MFR(1)) is preferably 3 or more. When MFR(2) / MFR(1) is 3 or more, for example, when producing a laminated sheet by coextrusion, the fluidity of the outer layer can be further increased, so that the surface roughness at the interface between the inner layer and the outer layer can be further reduced. Thereby, the color unevenness of the wood grain tone in the laminated sheet can be further suppressed. The upper limit value of MFR(2) / MFR(1) is not particularly limited, but from the viewpoint of moldability, it can be, for example, 10 or less.

[0058] Specifically, the MFR of the second propylene-ethylene block copolymer is preferably 0.7 g / 10 min or more and 2.7 g / 10 min or less, more preferably 1.0 g / 10 min or more and 2.4 g / 10 min or less. When the MFR of the second propylene-ethylene block copolymer is at least the lower limit value, the appearance of the laminated sheet can be further improved. When the MFR is at most the upper limit value, the heat resistance of the laminated sheet can be better maintained.

[0059] The Charpy impact strength (notched) at -20 °C of the second propylene-ethylene block copolymer according to JIS K 6921-2:2018 (ISO 19069-2:2016) is 5.0 kJ / m 2 g or more and 9.0 kJ / m 2 or less, preferably 6.0 kJ / m 2 g or more and 8.0 kJ / m 2 or less, more preferably. When the Charpy impact strength (notched) of the second propylene-ethylene block copolymer is at least the lower limit value, the cold resistance of the laminated sheet can be further improved. When the Charpy impact strength (notched) is at most the upper limit value, the heat resistance of the laminated sheet can be better maintained.

[0060] The content of the second propylene-ethylene block copolymer contained in the outer layer is preferably 70% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less, based on the outer layer.

[0061] 1-2-2. Other components The outer layer may further contain other components other than the second propylene-ethylene block copolymer as long as the effects of the present invention are not impaired. Examples of other components include the same ones as those in the inner layer. However, from the viewpoint of further improving the heat resistance and cold resistance of the laminated sheet, the content of other components in the outer layer is preferably as small as possible, more preferably less than 0.1% by mass, and even more preferably 0.01% by mass or less.

[0062] 1-2-3. Physical properties of the outer layer The thickness of the outer layer is not particularly limited. However, by making the thickness of the outer layer thinner than that of the inner layer, it is possible to improve the appearance of the laminated sheet and make it easier to exhibit the excellent properties exhibited by the inner layer.

[0063] The ratio of the thicknesses of the two outer layers is preferably 2.0% or more and 10.0% or less, more preferably 3.0% or more and 9.0% or less, and even more preferably 4.0% or more and 8.0% or less with respect to the total thickness of the laminated sheet. When the ratio of the thickness of the outer layer is 2.0% or more, the concealability of the inner layer containing a large amount of inorganic substance powder can be further enhanced, so that the appearance can be improved. When the ratio of the thickness of the outer layer is 10.0% or less, it is possible to more easily exhibit the characteristics of the inner layer.

[0064] The thicknesses of the two outer layers are each preferably, for example, 5 μm or more and 100 μm or less, and more preferably 8 μm or more and 90 μm or less.

[0065] 1-3. Physical properties of the laminated sheet The total thickness of the laminated sheet can be appropriately set according to the application. When the laminated sheet is used, for example, for a food packaging container, the total thickness of the laminated sheet is preferably 80 μm or more and 950 μm or less, and more preferably 100 μm or more and 900 μm or less.

[0066] 2. Manufacturing method of the laminated sheet The above-mentioned laminated sheet can be manufactured by any method. For example, the laminated sheet can be manufactured by a method of laminating a sheet-shaped inner layer and outer layer with a calendar roll, a method of co-extruding the inner layer and the outer layer, etc. As a method of co-extrusion, a method by a multilayer T-die method may be used, or a method by an extrusion inflation method using a plurality of annular dies may be used.

[0067] The manufactured laminated sheet may be stretched if necessary. When stretching, it can be stretched in a uniaxial direction, either longitudinal and / or transverse, or in a multi-axial direction. Thereby, the adhesion between layers, the surface appearance, and further the mechanical strength can be enhanced more.

[0068] 3. Molded body The above laminated sheet may be used as it is as a sheet-like material, or may be used as various molded bodies by molding by any molding method.

[0069] The molding method is not particularly limited, and examples include vacuum molding, pressure-air molding, match mold molding, etc. Among these, from the viewpoint of molding efficiency, vacuum molding is preferable. That is, the laminated sheet is preferably a laminated sheet for vacuum molding.

[0070] The molded body containing the above laminated sheet can be preferably used for various applications, such as packaging containers such as food packaging containers. Examples of food packaging containers include trays, cups, various containers, bags, etc.

Examples

[0071] Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples. The technical scope of the present invention is not limited by these.

[0072] 1. Preparation of materials 1-1. Polyethylene-based resin (A) (Linear low-density polyethylene (LLDPE) (A1)) · Manufactured by Prime Polymer Co., Ltd., SP0510, MFR (190 ° C, 2.16 kg) 1.2 g / 10 min (High-density polyethylene (HDPE) (A2)) · A2-1: Manufactured by Japan Polyethylene Co., Ltd., HB410R, MFR (190 ° C, 21.6 kg) 5.0 g / 10 min) · A2-2: Manufactured by Japan Polyethylene Co., Ltd., high-density polyethylene (MFR (190 ° C, 21.6 kg) 10.0 g / 10 min

[0073] The MFR of the polyethylene resin is the value measured at 190 °C, 2.16 kg or 21.6 kg in accordance with JIS K 6922-2:2018 (ISO17855-2:2016).

[0074] 1-2. Polypropylene resin (B) · B-1: Propylene-ethylene block copolymer (manufactured by Sun Allomer Co., Ltd., PB170A, MFR (230 °C, 2.16 kg) 0.35 g / 10 min, -20 °C Charpy impact strength (notched) 9.8 kJ / m 2 ) · B-2: Propylene-ethylene block copolymer (manufactured by Prime Polymer Co., Ltd., J702LJ, MFR (230 °C, 2.16 kg) 1.7 g / 10 min, -20 °C Charpy impact strength (notched) 7.0 kJ / m 2 ) · B-3: Homopolypropylene (manufactured by Prime Polymer Co., Ltd., E111G, MFR (230 °C, 2.16 kg) 0.5 g / 10 min)

[0075] The MFR of the polypropylene resin is the value measured at 230 °C, 2.16 kg in accordance with JIS K 6921-2:2018 (ISO19069-2:2016). The Charpy impact strength (notched) of the polypropylene resin is the value measured at -20 °C in accordance with JIS K 6921-2:2018 (ISO19069-2:2016).

[0076] 1-3. Inorganic substance powder (C) · Heavy calcium carbonate particles (manufactured by Takehara Chemical Industry Co., Ltd., SL-2200, average particle diameter 1.3 μm, no surface treatment)

[0077] The average particle diameter of the calcium carbonate particle group is the value specified based on the air permeability method in accordance with JIS M-8511.

[0078] 1-4. Other components (D) · D-1: Irganox 1010 (hindered phenol-based antioxidant) ·D-2: Irgafos 168 (Phosphorus-based antioxidant) ·D-3: CS-6CP (manufactured by Nitto Kasei Co., Ltd., 12-hydroxystearic acid soap, lubricant)

[0079] 2. Preparation and evaluation of laminated sheet 2-1. Preparation of laminated sheet (Examples 1 to 7, Comparative Examples 1 to 3) A three-layer laminated sheet having an inner layer and two outer layers on both sides thereof was prepared by a multi-layer co-extrusion T-die method so as to have the materials and compositions shown in Table 1. The thickness of the inner layer was 360 μm (90% of the total thickness of the laminated sheet), the thickness of the outer layer was 20 μm (5% each of the total thickness of the laminated sheet), and the total thickness of the laminated sheet was 400 μm.

[0080] In the table, the values shown in "outer layer" are the values in one outer layer. In this example, two outer layers having the same composition and thickness were provided on both sides of the inner layer.

[0081] 2-2. Evaluation (Cold resistance) The obtained laminated sheet was cut into 5 cm × 10 cm, cooled in a thermostatic bath set at -30°C for 1 hour or more, and then the falling weight impact strength was quickly measured using a DuPont impact tester (No. 451) manufactured by Toyo Seiki Co., Ltd. The mass of the falling weight was 0.3 kg to 1.0 kg, the radius of the impact center tip was 6.35 mm, the radius of the impact center receiving base was 6.35 mm, and the falling weight impact strength was determined as the value at 50% fracture and evaluated according to the following criteria. ◎: More than 1.5 J ○: More than 1.0 J and 1.5 J or less △: More than 0.5 J and 1.0 J or less ×: 0.5 J or less

[0082] (Heat resistance) After preheating the laminated sheet with a far-infrared heater, it was formed into a cup-shaped container with a bottom diameter of 40 mmφ and a height of 55 mm by a vacuum forming machine. The obtained container was filled with olive oil up to 50% of its volume and heated with a microwave oven until it reached 130°C. Then, the container was taken out and allowed to cool at room temperature for 30 minutes. After cooling, the appearance of the container was visually observed and evaluated according to the following criteria. ◎: No deformation occurred in the container. 〇: Slight deformation (less than 30% of the whole) occurred in the container. △: Some deformation (more than 30% and less than or equal to 60% of the whole) occurred in the container. ×: Clear deformation (more than 60% of the whole) occurred in the container.

[0083] (Vacuum formability (forming processability)) After preheating the laminated sheet with an infrared heater, it was formed into a cup-shaped container with a bottom diameter of 40 mm and a height of 55 mm by a vacuum forming machine. The appearance of the surface of the obtained container was visually observed, and the forming processability was evaluated according to the following criteria. ◎: The overall surface condition of the container was very good (no unevenness, wrinkles, protrusions, etc. occurred). 〇: The overall surface condition was good (no unevenness, wrinkles, protrusions, etc. occurred). △: The overall surface condition was generally good (unevenness, wrinkles, protrusions, etc. occurred partially). ×: The overall surface condition was poor (unevenness, wrinkles, protrusions, etc. occurred overall).

[0084] (Appearance) The appearance of the laminated sheet was visually observed and evaluated according to the following criteria. ◎: No color unevenness in the wood grain pattern occurred. 〇: Slight color unevenness in the wood grain pattern occurred. △: Partial color unevenness in the wood grain pattern occurred. ×: Overall color unevenness in the wood grain pattern occurred.

[0085] The evaluation results of Examples 1 to 7 and Comparative Examples 1 to 3 are shown in Table 1.

[0086]

Table 1

[0087] As shown in Table 1, it can be seen that the laminated sheet of Comparative Example 1 with a low content ratio of LLDPE in the inner polyethylene-based resin has low cold resistance. Also, it can be seen that the laminated sheet of Comparative Example 2 with the outer polypropylene-based resin being homopolypropylene also has low cold resistance. Further, it can be seen that the laminated sheet of Comparative Example 3 in which the inner polyethylene-based resin does not contain HDPE has protrusions and wrinkles on the surface of the molded body and low vacuum formability.

[0088] On the other hand, it can be seen that the laminated sheets of Examples 1 to 7 have good cold resistance while maintaining heat resistance. Also, it can be seen that the containers molded from the laminated sheets of Examples 1 to 7 have no protrusions or wrinkles on the surface and exhibit good vacuum formability. Further, it can be seen that the laminated sheets of Examples 1 to 7 do not have uneven color in the wood grain pattern and exhibit good appearance.

[0089] In particular, it can be seen that the higher the ratio of LLDPE to HDPE in the inner layer, the higher the cold resistance (comparison of Examples 1 to 3). Also, it can be seen that the higher the ratio of the MFR(2) of the second propylene-ethylene block copolymer in the outer layer to the MFR(1) of the first propylene-ethylene block copolymer in the inner layer, the less rough the interface between the inner layer and the outer layer and the more the uneven color in the wood grain pattern can be reduced (comparison of Example 1 and 4). Also, it can be seen that although the cold resistance tends to decrease as the content ratio of calcium carbonate increases, the allowable range can be maintained (comparison of Examples 1, 5 and 6). Also, it can be seen that the lower the MFR of HDPE, the better the vacuum formability can be maintained (comparison of Example 1 and 7).

[0090] From these facts, it can be seen that the laminated sheets of Examples 1 to 7 have high cold resistance while having good heat resistance and moldability.

Industrial Applicability

[0091] The laminated sheet of the present invention has high cold resistance while having good heat resistance and moldability. Therefore, the laminated sheet is suitable for food packaging containers and the like.

Claims

1. A laminated sheet having an inner layer and two outer layers laminated on both sides of the inner layer, wherein the inner layer contains a thermoplastic resin and an inorganic substance powder in a mass ratio of 10:90 to 60:40, the thermoplastic resin contains a polyethylene-based resin and a polypropylene-based resin in a mass ratio of 7:3 to 5:5, the polyethylene-based resin contains linear low-density polyethylene and high-density polyethylene, the polypropylene-based resin contains a first propylene-ethylene block copolymer and / or a propylene homopolymer, with respect to the total amount of the thermoplastic resin, the content of the linear low-density polyethylene is 30% by mass or more and 57% by mass or less, the content of the high-density polyethylene is 3% by mass or more and 30% by mass or less, the content of the first propylene-ethylene block copolymer and / or the propylene homopolymer is 30% by mass or more and 50% by mass or less, each of the two outer layers contains a second propylene-ethylene block copolymer, a laminated sheet.

2. The polypropylene-based resin consists of a first propylene-ethylene block copolymer, the laminated sheet according to Claim 1.

3. The inner layer contains a thermoplastic resin and an inorganic substance powder in a mass ratio of 10:90 to 50:50, the laminated sheet according to Claim 1.

4. The MFR(2) of the second propylene-ethylene block copolymer measured at 230 °C and 2.16 kg according to JIS K 6921-2:2018 (ISO19069-2:2016) is higher than the MFR(1) of the first propylene-ethylene block copolymer measured at 230 °C and 2.16 kg in accordance with JIS K 6921-2:2018 (ISO19069-2:2016), the laminated sheet according to Claim 2.

5. The ratio of the MFR(2) to the MFR(1) (MFR(2) / MFR(1)) is 3.0 or more, the laminated sheet according to Claim 4.

6. The MFR(1) is 0.2 g / 10 min or more and 0.5 g / 10 min or less, The Charpy impact strength (notched) at -20°C of the first propylene-ethylene block copolymer conforming to JIS K 6921-2:2018 (ISO 19069-2:2016) is 7.8 kJ / m ２ or more and 11.8 kJ / m ２ or less. the laminated sheet according to Claim 4.

7. The MFR(2) is 0.7 g / 10 min or more and 2.7 g / 10 min or less, The Charpy impact strength (notched) at -20°C of the second propylene-ethylene block copolymer conforming to JIS K 6921-2:2018 (ISO 19069-2:2016) is 5.0 kJ / m ２ or more and 9.0 kJ / m ２ or less. the laminated sheet according to Claim 4.

8. The MFR (L) measured at 190 °C and 2.16 kg in accordance with JIS K 6922-2:2018 (ISO 17855-2:2016) of the linear low-density polyethylene is 0.7 g / 10 min or more and 1.7 g / 10 min or less. The laminated sheet according to claim 1.

9. The MFR (H) measured at 190 °C and 21.6 kg in accordance with JIS K 6922-2:2018 (ISO 17855-2:2016) of the high-density polyethylene is 3.0 g / 10 min or more and 7.0 g / 10 min or less. The laminated sheet according to claim 1.

10. The inorganic substance powder is heavy calcium carbonate. The laminated sheet according to claim 1.

11. The average particle diameter of the heavy calcium carbonate is 0.7 μm or more and 6.0 μm or less. The laminated sheet according to claim 10.

12. The thicknesses of the two outer layers are each 2.0% or more and 10.0% or less of the total thickness of the laminated sheet. The laminated sheet according to claim 1.

13. Including the laminated sheet according to any one of claims 1 to 12. Food packaging container.

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